Some conventionally known vehicles rely on a motor generator (operable both as an electric power generator and as an electric motor) for their drive power. Among these vehicles are hybrid cars (hybrid vehicles) and electric cars (electric vehicles) disclosed in Patent Literatures 1 to 3 listed below. For example, a hybrid car has a gasoline, diesel, or other type of internal combustion engine and a motor generator running both on electric power generated by the output of the engine and on electric power stored in a battery (electric storage device) so that the car can travel by relying on either or both of these engine and motor generator for drive power.
In a vehicle equipped with a motor generator as a drive power source, the motor generator may be operated as an electric motor to supply drive power (motoring state) or, during deceleration of the vehicle, as an electric power generator to regenerate electric power which is saved in a battery. Since the battery has a limited storage capacity (the battery is capable of storing a limited quantity of electric power), the state of charge (SOC) of the battery is monitored to prevent overcharging of the battery, and the battery input is restricted (referred to generally as “Win restriction,” or maximum charging power restriction) if necessary while the motor generator is generating power.